Paint of virtually any color may be custom mixed by adding precisely measured amounts of one or more differently colored paint colorants to a base. The color of paints can be greatly affected by small variations in the amount of colorant added. Consequently, paint colorant dispensers must provide precise, repeatable, settings.
A paint colorant dispenser typically has a reservoir and a metering device which allows the user to accurately dispense a desired quantity of paint colorant. The reservoir is typically a canister capable of holding 1 or 2 liters of paint colorant. Manual paint colorant dispensers are commonly used in paint stores, hardware stores, and other establishments where small batches of colored paint are prepared. In such dispensers the metering device typically includes a pump having a piston movable within a measuring cylinder. A valve allows an operator to selectively place the interior of the measuring cylinder either in fluid communication with the paint colorant reservoir or in fluid communication with an outlet nozzle. An adjustable stop limits the travel of the piston within the measuring cylinder.
To dispense a measured quantity of paint colorant, an operator sets the stop at a position which corresponds to the desired quantity, sets the valve to place the interior of the measuring cylinder in fluid communication with the reservoir and then moves the piston along the measuring cylinder until it is prevented from travelling further by the stop. The operator then switches the valve to a dispensing position in which the interior of the measuring cylinder is in fluid communication with the outlet nozzle. Finally, the operator pushes the piston along the measuring cylinder to expel the measured quantity of paint colorant through the outlet nozzle. The amount of paint colorant dispensed is determined by the stroke of the piston (as limited by the stop) and the bore of the cylinder.
A typical paint coloring station has several (typically between 10 and 16) paint colorant dispensers each containing a different paint colorant so that a user can rapidly add precise amounts of several different paint colorants to a base to obtain a desired color.
One problem with existing paint colorant dispenser technology is that different units of measure are used in different parts of the world to measure volumes of paint colorant. To enable quick and accurate metering of paint colorants it is generally desirable that a paint colorant dispenser have a stop for which the discrete stop positions correspond to the locally used units of measure. Even in the same geographical region it may be desirable to provide different discrete stop locations for different colorants. For example, a more finely graduated stop might be desirable in a dispenser for paint colorants which are typically used in smaller quantities whereas a stop having fewer, more widely separated discrete positions might be desirable in a dispenser used for colorants which are typically used in larger quantities.
The need to provide stops which are calibrated in different units provides a difficulty for the manufacturers of paint colorant dispensers. Existing paint colorant dispensers have gauge rods having precisely located holes which define the stop positions. The gauge rods can be removed and replaced to alter the stop positions. Such gauge rods tend to be expensive to make. In some cases a gauge rod may have fifty or more holes. Making parts with a great many precisely located holes tends to be expensive even with modern manufacturing methods. Consequently, it is not possible to provide paint colorant dispensers which include interchangeable gauge rods as cost effectively as would be desired.
Another disadvantage of currently available paint colorant dispensing technology is that paint colorants can be very messy if they escape from containment. The valves in a paint colorant dispenser must be made very precisely to avoid any leakage of paint colorant. Manufacturing valve parts to very close tolerances is expensive. Even where valves are precisely made, some paint colorants are quite abrasive and tend to cause significant wear in valves. There is a need for a type of valve suitable for use with manual paint colorant dispensers which can operate smoothly and without leakage and yet is not unduly expensive to fabricate and service.
A further disadvantage of prior art manual paint colorant dispensers is that paint colorants, by their nature, are affected by contact with air and can dry out. Typically after paint has been dispensed through the dispensing nozzle of a paint colorant dispenser a small droplet of paint remains on the nozzle. More paint colorant remains inside the nozzle after paint colorant has been dispensed. There is a need for reliable means to seal off the nozzle of a paint colorant dispenser after use to prevent paint colorant within and adhering to the nozzle from drying out between uses.
A further problem with prior art paint dispensers is that typically the discrete stop positions do not provide fine enough increments in cases where it is necessary to dispense only very small quantities of paint colorant. Tinting formulae for making particular colors of paint typically specify the amounts of different colorants to add to one gallon of base material to achieve the desired colours. The amounts of each paint colorant in the formula must be proportionally reduced to tint a smaller amount of base material. For example, the amounts of colorant specified by a formula for making 1 gallon of paint must be divided by 8 if only one pint of paint is being tinted. As a result it is often necessary to accurately measure very small quantities of paint colorant.
In general, with a paint colorant dispenser having a stop which can be fixed only in discrete stop positions which permit dispensing paint colorant in multiples of one unit, it is not easily possible to dispense a fraction of a unit of paint colorant. For example, many paint colorant dispensers are calibrated in units of 1/48 fluid ounce. With such paint colorant dispensers it is not easy to accurately dispense 1/96 fluid ounce or 1/192 fluid ounces of paint colorant. Some prior paint colorant dispensers approach the problem of accurately dispensing small amounts of paint colorant by requiring the user to replace a gauge rod in the stop assembly with a separate gauge rod. The separate gauge rod allows the stop to be fixed in a position which allows only a small volume of colorant to be dispensed. A problem with this approach is that the dispenser should be separately calibrated for use with the separate gauge rod. Also, the separate gauge rod is easily lost. Installing the separate gauge rod during the dispensing process introduces extra steps and raises the possibility of errors. Other paint colorant dispensers have a separate pump for dispensing small volumes. Both of these approaches significantly increase manufacturing costs.